Role of Cell Type-Specific Molecular Rhythm Disruption in Alcohol Use Disorder

University Of Pittsburgh At Pittsburgh, Pittsburgh PA

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Abstract

PROJECT SUMMARY/ABSTRACT Alcohol use is a causal factor in over 200 health conditions and is estimated to account for 5.1% of global burden of disease and injury. Despite the enormous public health impact, we still lack a basic understanding of the mechanisms that contribute to alcohol use disorder (AUD). A prominent feature of AUD is circadian rhythm disturbances, including altered physiological rhythms and sleep/wake cycles. The relationship is bidirectional, as rhythm disruptions can exacerbate alcohol consumption and polymorphisms in canonical circadian genes associate with increased alcohol use. However, very little is known about the mechanisms underlying these relationships, especially at the molecular level in the brains of individuals with AUD. Molecular rhythms are generated by transcriptional-translational feedback loops to control circadian-dependent (near 24-hour) gene expression. Notably, AUD is associated with disrupted molecular rhythms of canonical circadian genes in the periphery and rodent studies have shown that disruptions to molecular rhythms in the striatum, particularly the nucleus accumbens (NAc), are associated with altered reward regulation and increased risk for substance use. Measures of molecular rhythms in human postmortem brain, however, have historically been challenging since each brain represents a single circadian timepoint. An innovative analysis uses “time of death” (TOD) to fit subjects on a 24-hr ‘clock’; by combining expression data from all subjects, it is possible to reconstruct molecular rhythm patterns in the human postmortem brain. To investigate AUD-associated molecular rhythm alterations, we performed a preliminary study examining large-scale transcriptional changes in bulk NAc tissue from subjects with AUD compared to controls. Notably, core circadian genes (e.g., CRY1, PER2), which display rhythmic expression in control subjects, were arhythmic in AUD, suggesting a molecular link to behavioral rhythm alterations observed in AUD patients. However, the NAc is composed of a variety of transcriptionally distinct cell types with differential roles in alcohol drinking behavior, and the role of molecular rhythms in these cell types has not been previously investigated. The central hypothesis of this R21 proposal is that molecular rhythms are disrupted in a cell-type specific manner in the NAc of AUD subjects, and that these disruptions contribute to excessive drinking. To test this hypothesis, we will use single nucleus RNA-sequencing (snRNA-seq) of human postmortem NAc tissue to determine how molecular rhythms are altered in heterogenous cell populations in AUD (Aim 1). We will then manipulate rhythms in specific NAc cell types to determine a causal role for rhythm disruption in alcohol drinking (Aim 2). Together, these studies will be the first to examine cell type-specific rhythms in human striatum, how they are altered in AUD, and their contribution to excessive alcohol consumption. These studies are central to understanding the mechanisms underlying circadian disruptions in AUD and may result in the discovery of novel therapeutic targets and/or time-dependent strategies for future treatments.